The printing industry in general finds many applications for the use of water-based inks and overprint varnishes as a means of meeting increasingly stringent solvent effluent regulations. Present day water-based inks often fail to satisfy these regulations as well as the necessary printability, stability, and performance properties required for commercial inks. For example, the various ethylene-acrylic acid copolymer salts of U.S. Pat. No. 3,607,813, the disclosure of which is incorporated herein by reference (for the printing process descriptions therein), in addition to requiring complex polymer and ink preparations, lack in performance on certain substrates. Other such aqueous or semi-aqueous systems proposed for printing inks contain polymers such as styrene-butadiene or polyacrylate latex systems, but these systems also have serious drawbacks including being non-water dispersible after short drying periods which complicates equipment clean up. Other water soluble or dispersible polymers suggested for printing ink use are discussed in U.S. Pat. No. 4,072,644.
The present invention provides marked improvements in the preparation, stability, and performance of water-based inks for printing and coating, particularly in regard to flow-out, wet-out, viscosity modification, color development, reduction in surface tension, pick-up on the printing rollers or other mechanisms, and greatly improved adhesion on certain substrates such as aluminum. In particular, the inks of the present invention containing polyvinyl alcohol have a substantial increase in optical density as compared to a comparable, control ink without polyvinyl alcohol when flexo printed onto polyethylene. These improvements are particularly dramatic in comparison to the effects of known additives such as hydroxyethylcellulose and the like on aqueous inks.